THE BASIS OF LIFE 19 



already as the termination of the names of albuminoids e.g., 

 gelatin, chondrin, mucin. 



The various ferments are substances which protoplasm sets 

 aside for specific purposes. Primitively, contact with the 

 substance to be fermented determined the nature of the ferment 

 assigned to the task. There are reasons for thinking that proto- 

 plasm still retains its power of making a suitable response ; 

 cases may be cited in which the lock presented to protoplasm 

 shapes the wards of the key. In such cases the fermentable 

 substance provokes the formation of the ferment. But, for the 

 most part, in situations where particular ferments are regu- 

 larly needed, protoplasm has acquired the habit of making 

 such ferments and no others. The cells of salivary glands accu- 

 mulate ptyalin, the cells of gastric glands accumulate pepsin, 

 during the intervals between meals. 



The capacity of protoplasm for producing a new ferment 

 when it is needed is shown by such examples as the following : 

 Blood-plasm contains a variety of proteid substances. If a 

 solution of white of egg be added to it, the mixture is clear 

 and uniform. Yet egg-albumin is treated by the blood as a 

 foreign body, a poison. When injected into the veins of a 

 living animal, some of it is excreted by the kidneys, some 

 destroyed in the blood-stream. If several successive doses of 

 egg- albumin are injected into an animal (it is most convenient 

 to inject it into the peritoneal cavity), the power of the 

 blood to destroy the intruder is greatly increased. If now 

 a specimen of blood be taken, and the plasma or serum mixed 

 with egg-albumin, the mixture is no longer clear. The egg- 

 albumin is precipitated. The blood of the animal thus " pre- 

 pared " has developed a ferment, termed a " precipitin," which 

 throws down egg- albumin. If instead of egg- albumin, which, 

 although a foreign body, is comparatively innocent, a substance 

 which is distinctly poisonous, toxic, be injected into an animal, 

 the first dose, if a large one, will prove fatal. If, however, the 

 first dose be small, and succeeding doses progressively larger, 

 the animal acquires the power of tolerating a quantity of 

 the poison much larger than would have proved fatal in the 

 first instance. A classical example of this, because it afforded 

 an opportunity of directly observing under the microscope the 

 difference between " unprepared " blood and blood from an 



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